An air pressure adjusting device is a device that adjusts an air pressure of a pneumatic tire mounted on a vehicle. This air pressure adjusting device adjusts an air pressure of a pneumatic tire while a vehicle is running based on a target air pressure calculated by running conditions of the vehicle (for example, vehicle speed, running path, road surface condition, and the like). By this, fuel economy and running performance of the vehicle are improved.
Additionally, as the air pressure adjusting device, there is an air pressure adjusting system provided with an air pressure supply device described in Japanese Unexamined Patent Application Publication No. 2009-056948. The air pressure adjusting system described in Japanese Unexamined Patent Application Publication No. 2009-056948 is provided with a mechanism that supplies air to a pneumatic tire and has inside a hub unit and a wheel an air passage for introducing compressed air in the pneumatic tire.